1. Field of the Invention
The present invention relates to a method for operating a gas turbine installation, and to a gas turbine installation.
2. Brief Description of the Related Art
It is known from the prior art that the mass flow of the compressor can be cooled to increase the power of gas turbines. Cooling of the mass flow of air which is taken up by the gas turbine leads to an increased power output from the turbomachine. The reasons for this are firstly the increased mass flow of air resulting from the cooling and also the reduction in the power consumption of a compressor device at lower inlet temperatures. In principle, two types of cooling are known, cooling of the inlet air which flows into the compressor, and intercooling between two separate compressor stages.
Intercooling of the air during compression, as is known from DE A1 42 37 665, reduces the power consumption of a turbo-compressor as a result of a reduction in the compression work. In this case, however, unlike with inlet cooling, there is no increase in the mass flow of air. In most cases, conventional heat exchangers are used for the intercooling.
In recent times, there have been increased efforts to achieve the desired cooling both in the case of inlet cooling and in the case of intercooling, by the injection of water. For intercooling, this is known, for example, from EP-A1 0 770 771. This, however, uses exclusively the concept of cooling by evaporation, in which finely atomized, demineralized water is added to the air flow. In the case of intercooling, this takes place in the interior of the compressor means between individual compressor stages (known as “spray intercooling”), whereas in the case of inlet cooling this takes place as early as upstream of the compressor means, in the air inlet. The addition of drops of water means that the compressor is partially operated “wet”, i.e. with a 2-phase medium, downstream of the location where the drops are added. Even for relatively small quantities of injected water of only 1-1.5% (based on the intake mass flow of air), the wet region of the compressor may extend over 5-8 stages. The length of the wet compressor part is not only a function of the quantity of water added but also is dependent on the drop size spectrum and on the air inlet temperature. Only after complete evaporation of the water does the compressor return to operation with dry gas. In previous “wet” operation of the compressor, no special precautions are taken making it possible to determine which drop size spectrum is present in the air sucked in by the compressor and which drop size spectrum is established within the compressor. Whereas the drop size spectrum in the intake air stream is dependent on the spray technique used, the velocity distribution in the air inlet and the positioning of the spray device, the drop size spectrum (which constantly changes in the downstream direction) in the compressor is influenced by the pressure change in the compressor means, the increase in temperature and, in very general terms, by the aerodynamic properties of the flow in the compressor means.
Particular difficulties arise when using the “wet” operation of a compressor from the fact that the drops in the compressor on the one hand may strike blades and vanes and other surfaces at a high velocity and on the other hand lead to the formation of films of water on the blades and vanes and on the casing. This entails a range of problems, of which just four are to be mentioned here by way of example:
(I) the aerodynamic properties of the blades and vanes change,
(II) water can penetrate into cooling air lines and other components of the cooling air system and have an adverse effect on the turbine cooling,
(III) existing pressure and temperature sensors give different measurement results depending on whether they are dry or wet,
(IV) the impinging water drops may erode the blades and vanes and other structure parts and lead to increased corrosion through film formation. In this context, the type and extent of the film formation and also the strength of the drop impingement are highly dependent on the drop size spectrum in the two-phase flow.
These examples demonstrate that it is of great interest for monitoring of the gas turbine and of the “wet” operation of the compressor—and therefore with a view to ensuring reliable operation—to detect liquid water which is present in the compressor and in the secondary air system and/or to enable the drop size spectrum in the flow passage of the compressor to be determined. However, the measurement devices which have hitherto been installed in commercially available gas turbine installations are unsuitable for this purpose. Reliable determination of the presence of water in the compressor, the determination of the extent of the wet region and/or the drop size spectrum in the compressor is not therefore currently possible in installations of this type.